Bathrooms get a cleanup

Bathroom installation regulations have perhaps always been somewhat contentious and have undergone a number of changes in requirements in the past 10 years. The requirements have again changed in the 17th Edition of BS 7671 and indeed have become simpler. This part now harmonises with the corresponding CENELEC part, and introduces some significant changes for the UK.

Part 7 of BS 7671: 2008 makes specific references to electrical installations in areas defined as ‘special installations or locations’ in which bathrooms or showers are included. While complying with the general requirements of BS 7671, some further requirements or restrictions apply to installations in these rooms.

In a bathroom or shower room the increased risks are from exposed wet skin, which has a lower contact resistance, the splashing and ingress of water, and the close proximity of earthed metalwork.

Zone concept

The concept of zones was introduced into BS 7671 for the 2001 edition and allowed different rules to be applied to different zones. The zone concept remains in BS7671, but zone 3 has been removed.

This is one of the most significant regulation changes in the whole of the 17th Edition document. Without a zone 3, there are no specific rules for zone 3 and only the general rules apply. Hence equipment can be installed at the boundary of zone 2.

The zones can be summarised:

• Zone 0 is the bath or shower tray.
• Zone 1 can be considered to be the area where the individual is bathing or showering, or the area where shower water is likely to be directly sprayed.
• Zone 2 is the area beyond zone 1, extending by a further 600 mm.

Outside zone 2 the general rules of the standard apply, but in reality, virtually any equipment can now be installed outside zone 2. The zones provide a means of controlling the location type and environmental rating of electrical equipment installed in a bathroom or ‘locations containing a fixed bath or shower’, such as bedrooms, changing facilities or sports clubs.

These will require different design solutions from those for a domestic bathroom, and in all cases, full consultation with the client’s advisers and equipment manufacturers is essential.

Electric shock requirements

The requirements in addition to the general rules can be summarised:

• All circuits must have a 30 mA residual-current device (RCD).
• Socket outlets must be 3 m from the outer limit of zone 1, except installations using separated or safety extra-low voltage (SELV).
• With main equipotential bonding, no local supplementary bonding is required.
• Obstacles and equipment that is ‘out of reach’ are not permitted.
• A non-conducting location or earth-free local equipotential bonding are not allowed.
• Electrical separation can only be used for single items.
• For SELV and protected extra low voltage (PELV), basic protection must be used.

All circuits supplying the bathroom are now to be provided with additional protection by the use of an RCD with a rated residual operating current not exceeding 30 mA. However, where this is provided, supplementary equipotential bonding is not required.

The use of RCDs on all circuits, including lighting circuits, may cause some problems initially – possible increased risk of hazards if lights go out unexpectedly. These can be overcome relatively easily with some planning: the bathroom can be put on on a separate lighting circuit, or two lighting circuits can be put on the bathroom and surrounding rooms.

The new requirements of the 17th Edition are not retrospective. In this edition, however, supplementary equipotential bonding is not required in bathrooms, provided each circuit is given additional protection by an RCD sensitivity not exceeding 30 mA.

This will be the preferred solution in new developments, but there are many existing dwellings and other locations with bath and shower facilities that already have this bonding. When bathrooms are modified or refurbished, it may be more economic to extend or modify this, rather than rewire and install RCDs.

Equipment selection and erection

The equipment requirements are summed up below, and they fall into two types of regulation – ingress protection and suitability with regards to switches and accessories.

• Equipment in zone 0 must be to IP X7.
• Equipment in zones 1 and 2 must be to IP X4.
• Equipment exposed to cleaning jets must be to at least IP X5.
• In zone 0, no switchgear or accessories are allowed.
• In zone 0, only 12 V current-using equipment complying with a relevant standard is allowed.
• In zone 1, only 12 V SELV switchgear or accessories are allowed.
• In zone 1, only whirlpool units, electric showers, shower pumps, ventilation equipment, towel rails, water heaters, luminaires and 25 V SELV or PELV equipment is allowed.
• In zone 2, SELV switches and socket outlets and shaver supply socket outlets to BS EN 61558-2-5 are the only permitted switchgear or accessories.

The general principle of this group of regulations is that unsuitable electrical equipment must not be accessible to persons in the bath or shower, when they are in zone 1. This is deemed to be outside zone 2.

The ‘inaccessibility’ principle extends to electrical equipment generally, and only switches using insulated linkages or pull cords to operate BS 3676 devices or specially designed controls to BS 456 (instantaneous water heaters) are permitted within the zones.

In general, those responsible for selection and erection of equipment will find that Class II devices more readily satisfy the requirements for bathrooms.

With the increased use of pumped water in bathrooms for spa-baths, power showers and so on, there is a need, on occasion, to provide for motive power within the area of the bath. In order to protect against direct and indirect contact, supplies for such equipment must be by SELV, and the nominal voltage must not exceed 12 V rms.

Where it is necessary to mount the SELV source within the bath enclosure, it may only be accessible using a tool. The reason for this is concerned with the now familiar definition of a ‘skilled person’: it is assumed that persons using a tool to access the SELV source under a bath will be sufficiently informed and skilled to avoid danger, and the circuit will be dead and isolated before the work is commenced.